1. Field of the Invention
This invention relates to an NAS (network attached storage) system and, particularly, to technology which provides the client computers with means for monitoring faults in the system.
2. Description of the Related Art
In recent years, the quantity of data handled on the internet has strikingly increased and data storage has become more important. When accumulated, increased, integrated and unified, the data offer enhanced additional value, and the accumulated data receive expanding demands.
Storage area network (SAN)-connected disk array subsystems have heretofore been introduced into the data storage market, and attempts have been made to integrate and unify the data relying upon the scalability in both performance and capacity and upon a variety of intelligent functions. In recent years, the data storage system has been expanded to a network attached storage (NAS) device and to a file server that attempts to unify the data so that the data can be favorably used by sharing the file among client computers that are spanning dissimilar platforms.
Technologies related to storage servers connected to the network have been specifically disclosed in Japanese Patent Laid-Open Nos. 5617/2001, 84112/2001 and U.S. Pat. No. 5,781,716. According to Japanese Patent Laid-Open Nos. 5617/2001, 84112/2001, the client computers and the file server are connected through a LAN (local area network), and the file server is connected to a storage control unit.
According to U.S. Pat. No. 5,781,716, file servers connected to a local area network (LAN) are connected to client computers that are not shown. The file servers monitor each other. When the file server on one side breaks down due to a fault, the remaining file server takes over the processing to continue the file input/output processing to and from the client computers, thus constituting a fault tolerant system. In the technologies of all of these publications, however, the client computers and the file servers are connected through a LAN, and the storage system is connected to the file servers.
An advantage of NAS is that a file server function exists between the client computers and the storage system, and that the hardware structure of the storage system need not be taken consideration and can thus be concealed. When concealed, however, it becomes difficult to detect a fault in the storage system though a fault, so far, could have been directly detected from the host computer.
In a network system equipped with two file servers that monitor each other for their states and take over the processing of the file server that has become faulty as is done in U.S. Pat. No. 5,781,716, it becomes more difficult to detect the fault and to locate the faulty part. Namely, it becomes difficult to distinguish whether the fault is in the file server, in the LAN connecting the client computers to the servers or in the interface between the file servers and the storage.
In the technologies disclosed in Japanese Patent Laid-Open Nos. 5617/2001 and 84112/2001, in a case where the file is not accessible from the client computer, it is not possible to distinguish whether a fault is in the file server or in the data storage system. In addition, there is no means for fault notification. Further, if reference is made to a log file in a client computer, which appears to be free of fault, there have been, in many cases, recorded errors in the application that operates on the client computer, errors in the host bus adapter and in other hardware, and various error data from the data storage system. Such data can become known only through a particular means for providing notice to an external unit, such as a fault monitoring device. A fault is often found for the first time only after the client computer has broken down. Further, a conventional computer system in an open environment includes a protocol through which a computer receives a notice from the data storage system and an AEN (asynchronous event notification), which is a notice of asynchronous event. When a similar environment is expressed by an SCSI (small computer system interface) standard, there is a protocol through which the initiator receives a notice from a target. However, the above protocols have not been widely used, and are not enough to serve as means for fault notification to the client computers connected to the network.